1. Field of the Invention
The present invention relates to a membrane-electrode assembly for a fuel cell, a method of making the same, and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen included in a hydrocarbon-based material such as methanol, ethanol, natural gas, etc.
Fuel cells provide a clean energy source that can replace power generation systems that burn fossil fuels. A typical fuel cell includes a stack composed of unit cells and produces various ranges of power output. Since it has four to ten times more energy density than a small lithium battery, the fuel cell may be utilized as a small portable power source.
Representative exemplary fuel cells include polymer electrolyte membrane fuel cells (PEMFC) and direct oxidation fuel cells (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol (DMFC) as a fuel.
In operation, a fuel of a fuel cell is supplied to an anode of the fuel cell and adsorbed on a catalyst layer (or catalysts) of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into a cathode of the fuel cell via an external circuit, and the protons are transferred into the cathode through a polymer electrolyte membrane between the anode and the cathode. In addition, an oxidant is supplied to the cathode, and then the oxidant, protons, and electrons are reacted on a catalyst layer (or catalysts) of the cathode to produce electricity along with water.
The catalyst layer of the anode and/or the catalyst layer of the cathode is formed only in a set or predetermined area of the polymer electrolyte membrane by using a metal mask. However, a lot of time is required in using (or placing) the metal mask to form a catalyst layer, and the metal mask may cause a shadow effect in which the catalyst layer is not formed on an edge portion of an upper surface of the catalyst layer because it is shielded by the metal mask due to the thickness thereof.